Drilling fluids can be used in geotechnical engineering but also in other fields. When used in geotechnical engineering, a drilling fluid or mud is a specially designed fluid that is circulated through a wellbore as the wellbore is being drilled to facilitate the drilling operation. Drilling operations in general can concern oil and gas production or the generation of drilling holes useful in exploiting geothermal activity. The various functions of a drilling fluid include removing drill cuttings from the wellbore, cooling and lubricating the drill bit, aiding in support of the drill pipe and drill bit, and providing a hydrostatic head to maintain the integrity of the wellbore walls and prevent well blowouts.
An important property of the drilling fluid is its rheology, and specific rheological parameters are intended for drilling and circulating the fluid through the well bore. The fluid should be sufficiently viscous to suspend barite and drilled cuttings and to carry the cuttings to the well surface. However, the fluid should not be so viscous as to interfere with the drilling operation.
Drilling fluids for sinking wells in rock and bringing up the rock cuttings are flowable water- or oil-based systems that are thickened to a needed extent. Oil-based systems are acquiring increasing significance in practice and are used in particular in offshore drilling operations. Oil-based drilling fluids are generally used as so-called invert emulsion muds which generally consist of a 3-phase system: oil, water and fine-particle solids. Drilling fluids such as these can be preparations of the w/o emulsion type, i.e. the aqueous phase is heterogeneously and finely dispersed in the continuous oil phase. A range of additives may be used for stabilizing the system as a whole and for establishing the required performance properties, including in particular emulsifiers and emulsifier systems, weighting agents, fluid loss additives, viscosity adjusters and optionally an alkali reserve. Further details can be found, for example, in the Article by P. A. Boyd et al., “New base oil used in low toxicity oil muds”, Journal of Petroleum Technology, 1985, 137-142.
As mentioned, one key criterion for evaluating the usefulness of drilling fluids in practice are their rheological characteristics. Certain viscosity values have to be maintained in drilling fluid systems suitable for practical application. In particular, uncontrolled thickening and hence increases in the viscosity of the drilling fluid have to be strictly prevented because, otherwise, the pipe can become stuck during drilling (cf. Manual of Drilling Fluids Technology, NL Baroid/NL Inc. 1985, Chapter “Stuck Pipe”) and can only be freed by expensive, time-consuming measures. In practice, therefore, suitable diluents are added to the drilling fluid systems before and also during drilling. It is known from the prior art that anionic surfactants from the group of fatty alcohol sulfates, fatty alcohol ether sulfates and alkyl benzenesulfonates are preferably used for this purpose. It has been found in practice, however, that although compounds of this type can effectively influence the rheology of the drilling fluids, problems can arise with diluents known from the prior art when drilling fluids are used at low external temperatures. This applies in particular at temperatures of 50° F. (10° C.) and lower. There is invariably an increase in viscosity which is difficult or impossible to control, even when known diluents are used.
A second key criterion for the usefulness of drilling fluids is that the fluid functions as metalworking fluid to keep the metal parts operational.
In addition, all additives and auxiliaries used in offshore and onshore drilling fluid systems are expected to satisfy stringent biodegradability and toxicity requirements. Also, the ambient conditions prevailing during drilling operations, such as high temperatures, high pressures, changes in pH caused by the inrush of acidic gases, etc., impose high demands on the choice of possible components and additives.
The choice of emulsifiers for metalworking fluids and well servicing systems and, more particularly, drilling fluids is primarily directed at finding substances which lead to maximum stability of the emulsion, even under different conditions of practical application, e.g. breaking of the emulsion should be prevented. This applies in particular to emulsions of the water-in-oil type. It is furthermore generally advantageous if an emulsifier additionally suppresses excessive foaming of the emulsion.
Previously, ether carboxylic acids were used as emulsifiers (see e.g. US 2007 049 500). For the above reasons, there is a need for novel improved emulsifiers that meet the above outlined quality requirements.